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iOS UIImage clip to paths

Tags:

ios

uiimage

I'm working with an image where the user has selected part of it using UIBezierPath. How can I delete/clear out/make transparent everything that is not part of that selection?

like image 678
MB. Avatar asked Nov 29 '11 09:11

MB.


1 Answers

With one path it's very easy. Just set the path as the clipping path:

- (UIImage *)maskImage:(UIImage *)originalImage toPath:(UIBezierPath *)path {
    UIGraphicsBeginImageContextWithOptions(originalImage.size, NO, 0);
    [path addClip];
    [originalImage drawAtPoint:CGPointZero];
    UIImage *maskedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return maskedImage;
}

If you want to use the union of multiple paths, it's harder, because Quartz doesn't have any functions that directly compute the union of two paths. One way is to fill each path one by one into a mask, and then draw the image through the mask:

- (UIImage *)maskedImage
{
    CGRect rect = CGRectZero;
    rect.size = self.originalImage.size;
    UIGraphicsBeginImageContextWithOptions(rect.size, YES, 0.0); {
        [[UIColor blackColor] setFill];
        UIRectFill(rect);
        [[UIColor whiteColor] setFill];
        for (UIBezierPath *path in self.paths)
            [path fill];
    }
    UIImage *mask = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0.0); {
        CGContextClipToMask(UIGraphicsGetCurrentContext(), rect, mask.CGImage);
        [self.originalImage drawAtPoint:CGPointZero];
    }
    UIImage *maskedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return maskedImage;
}
like image 85
rob mayoff Avatar answered Nov 04 '22 11:11

rob mayoff